1. Field of Technology
The present disclosure relates to nickel-base alloys and articles of manufacture made therefrom. The present disclosure more particularly relates to nickel-base alloys having substantial thermal cracking resistance and other properties making the alloys suitable for use in die casting dies and in other articles of manufacture.
2. Description of the Background of the Technology
Die castings are produced by injecting molten metal under pressure into the cavity of a metal mold or die. (As used herein, “metal” refers to metals and metallic alloys.) The cavity imparts shape to the solidifying metal. There are four principal alloy systems that are commonly die cast. These include zinc, magnesium, aluminum, and copper (brass) alloy systems. The approximate casting temperatures for these systems are 800° F. (427° C.), 1200° F. (649° C.), 1250° F. (677° C.), and 1780° F. (971° C.), respectively. The performance of a casting die depends upon the material from which the die is made, the die heat treatment steps, and a number of non-material-related factors, including casting temperature, die geometry, and casting speed. In general, higher casting temperatures, greater die cavity complexity, and higher casting speeds degrade casting die performance. Casting dies fail predominantly by thermal fatigue or heat checking, where small cracks develop on the die surface after repeated thermal cycling. Stress corrosion cracking (SCC) and corrosion fatigue have also been identified as operative mechanisms of casting die failure and may significantly facilitate the development of thermal fatigue cracking. Therefore, high resistance to cracking, either due to thermal fatigue/thermal checking or other mechanisms, has been considered an important characteristic for high quality die alloys.
Casting dies are typically made of hot work tool steels. The most common die casting die alloy is H-13 steel (UNS T20813), which nominally includes, in weight percentages, 0.4 carbon, 5.25 chromium, 1.5 molybdenum, 1.0 vanadium, and balance iron. Maraging steels are also used, primarily for die components having relatively complex geometries that preclude the removal of the EDM recast layer. Other steel alloys used in die casting dies include mold steels and certain martensitic stainless steels.
Die casting dies are very expensive, and in some applications the die may cost more than the die casting machine itself. Therefore, die life is a major consideration in the die casting industry. Die life is typically measured in “shots” or number of parts, and 20,000 to over 200,000 parts per die is considered a typical die service lifetime. Thermal cracking is generally regarded as the most significant failure mode that limits die life. The steel alloys widely used in making die casting dies, however, have relatively limited thermal cracking resistance, requiring rather frequent replacement of the dies. Thus, developing a material having comparable mechanical properties and exhibiting significantly better thermal cracking resistance than conventional steel die casting alloys has been and continues to be a focus of research and development efforts.
Accordingly, it would be advantageous to provide an improved alloy having good mechanical properties and substantial resistance to thermal cracking, and that would be suitable for use in die casting die applications. It also would be advantageous to provide die casting dies and other tooling fabricated from such alloys.